The present invention relates to a radio-frequency (RF) shield for magnetic resonance imaging (MRI) systems and an MRI system. More particularly, the present invention relates to an RF shield capable of preventing degradation in MRI image quality caused by an eddy current included in the RF shield, and an MRI system employing the RF shield.
An MRI system has an RF shield interposed between an RF coil and gradient coils for the purpose of preventing the coupling among the RF coil and gradient coils. However, an eddy current deriving from a magnetic field gradient is induced in the RF shield, which degrades the MRI image quality.
In the past, the RF shield has been divided into portions in efforts to minimize the adverse effect of the eddy current (refer to, for example, Patent Document 1).
Moreover, deformation of the RF shield is prevented for fear that an asymmetric eddy current may be induced (refer to, for example, Patent Document 2).
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. Hei 8-252234
[Patent Document 2]
Japanese Unexamined Patent Application Publication No. 2000-333929
When an RF shield is grounded, the properties of an RF coil can be stabilized.
However, the geometric arrangements of an X-axis gradient coil, a Y-axis gradient coil, and a Z-axis gradient coil relative to the RF shield are different from one another. Therefore, an eddy current induced in the RF shield is different among the X-axis gradient coil, Y-axis gradient coil, and Z-axis gradient coil. If the RF shield is merely grounded, the eddy current cannot be released homogeneously. This leads to degradation in MRI image quality.